Disclosed is a method of preparing a polymerizable photoacid-generating monomer using a fluorinated sultone.
Advanced photolithographic techniques for imprinting desired patterns on silicon wafers generally rely upon acid-catalyzed deprotection of esters to acids in the poly(methacrylate) photoresist polymers as the key chemical reaction for transferring the pattern in order to induce a solubility change. This catalytic process, referred to as chemical amplification, is induced by irradiation of a photo-sensitive reagent or photoacid generator (PAG). PAGs used in photoresist polymers may consist of two parts: a sulfonate anion, and a tris(hydrocarbyl)sulfonium cation which usually has at least one aromatic group, where the cation absorbs a photon and decomposes to generate one acid proton, which leads to multiple desirable acid-catalyzed chemical reactions. Sulfonic acid superacids, e.g., alkyl or arylsulfonic acids having fluorine substituents generally within 2 or 3 bond lengths of the sulfur atom, are preferred in some applications.
As advances in photolithographic techniques lead to patterns with increasingly finer resolution, acid diffusion in the photoresist matrix becomes a concern. Acid diffusion may be impeded by, in one approach, tethering the conjugate base of the acid (e.g., a sulfonate anion) to the polymer, restricting the acid to a limited volume and more evenly distributing the PAG in the photoresist matrix.
U.S. Patent Application Publication No. 2009/0202943 A1 discloses a positive-tone resist which includes a polymer prepared from an acrylate or methacrylate monomer having a photoactive sulfonium fluoroalkylsulfonate salt (i.e., the conjugate base of a superacid) tethered to it through a (meth)acrylate monomer linkage. One exemplary such monomer is prepared by condensing the triaryl sulfonium salt of 1,1-difluoro-2-hydroxyethylsulfonate with (meth)acrylic anhydride. While such a condensation can in principle be used, the synthesis of the anion involves a three-step synthesis from commercially available precursors, and the precursors are limited due to the possibility of side-reactions with the cation and/or the polyfunctional anion.